Polybutadiene (PBD) is a soft, low modulus though tough, elastomeric polymer, generally unsuited as a coating for such materials as flooring, furniture, appliances, electronic components, motor vehicle parts and the like that require a hard, clear, scuff-resistant protective and glossy surface. However, polymers such as polybutadiene having molecular weights higher than about 3,000 g/M would be desirable for use in coatings since their relatively high molecular weight would result in less shrinkage upon curing than other materials having lower molecular weights.
Radiation-curable materials are desirable for their ease of curing. Such materials include (meth) acrylic and vinyl monomers from BASF, oligomers of polyesteracrylate, epoxy acrylate, and urethane acrylate from UCB Chemicals Corp., acrylate-terminated PBD from Sartomer Co., and Ro Shield.TM. of Rohm and Haas Company, as well as Ricacryl.RTM. 3100 and Ricacryl.RTM. 3500, methacrylated PBDs of Ricon Resins, Inc.
Such radiation-curable materials known to the art have many disadvantages. In general, ultraviolet curable coatings adhere to a narrow range of substrates and have low resistance to water, chemicals and solvents after curing. Those designed to form hard coatings tend to form brittle coatings, and those designed to form flexible coatings tend to form coatings that are too soft. Such materials are not soluble or dispersible in water and must often be mixed with toxic solvents or reactive diluents to decrease their viscosities enough for spraying or painting on a substrate, with consequent harm to the environment when the solvents evaporate. Reactive diluents may increase toxicity and sometimes prevent full curing initially, resulting in changing properties over time. Many radiation-curable materials are mixtures of adhesion agents, dispersion agents, plasticizers, cross-linking agents and wetting agents which must be specially compounded at the site of application. Further, in previously-known acrylate/methacrylate-functionalized polybutadiene-based radiation-curable resins, the acrylate functionalities are not optimized by number or type to provide sufficient crosslinking to produce hard, adherent or solvent-resistant coatings.
A number of radiation-curable resins have been described in the literature. U.S. Pat. No. 3,855,379 issued Dec. 17, 1974 to Araki et al. for "Novel Polybutadiene Derivative Curable with Ionizing Radiation" discloses radiation-curable coating materials made by reacting a polymeric butadiene with an isocyanate compound having a vinyl group. U.S. Pat. No. 4,224,357 issued Sep. 23, 1980 to Iwai et al. for "Method and Composition for Forming Electron Beam Curing High Build Coating" discloses making a high build coating film by mixing a polymerizable resin which has at least two polymerizable unsaturated double bonds and at least one hydroxyl group with a polyisocyanate and curing by irradiation.
Puskas, J. E., et al. (1988), "New polyisobutylene-based UV-curable flexible coatings," Polymer Bull. 20:253-260, discloses ultra-violet-curable coatings prepared from acrylate and methacrylate-capped linear or three-arm star polyisobutylenes in the presence of multifunctional acrylates or methacrylate esters.
Japanese Patent Publications No. 01020215 A and 01020216 A, both published Jan. 24, 1989 for "Photocurable Resin Composition" (abstracts) disclose photocurable resin compositionsmodified with a carboxylic acid-terminated rubber and having photo/radical-polymerizable functional groups on the molecular ends mixed with a compound having at least one dicyclopentenyl group or isobornyl group. Japanese Patent Publication No. 01020213 A published Jan. 24, 1989 for "Photocurable Resin Composition" discloses a polybutadiene resin obtained by mixing photocurable telechelic polybutadiene resin having photo/radical-polymerizable functional groups on the molecular ends with a reactive group such as phenoxypolyethylene glycol acrylate and adding a silane coupling agent. Japanese Patent Publication No. 02091111 A published Mar. 30, 1990 for "Photocurable Resin Composition" (abstract) describes a blended photocurable composition comprising a hydrogenated polybutadiene with a photopolymerization initiator and an unsaturated carboxylic acid derivative having phosphorus in the molecule.
None of the foregoing references disclose water-soluble or water-dispersible coating materials.
U.S. Pat. No. 3,841,895 issued Oct. 15, 1974 to Hick for "Flexible Hydrocarbon Rubber Substrate Finished with a Thermosetting Acrylic Enamel" and a divisional patent thereof, U.S. Pat. No. 3,959,554 issued May 25, 1976 to Hick for "Aqueous Thermosetting Acrylic Enamel for Finishing Flexible Hydrocarbon Rubber Substrates" disclose a composition comprising acrylic polymers, carboxylic acid polymers, and a heat-reactive condensate such as polyisocyanate, which can be neutralized to form a water-based finish with ammonia or an amine such as diethylethanol amine. These materials do not appear to be radiation-curable and the neutralizing amines do not contribute to the performance of the material.
Water-dispersible radiation-curable materials are described, for example, in U.S. Pat. No. 5,268,257 issued Dec. 7, 1993 to Mirle et al. for "Aqueous Developable, Photocurable Composition, and Flexible, Photosensitive Articles Made Therefrom" which discloses a water-dispersible composition prepared by reacting a solid carboxylated copolymer having at least one pendent carboxyl group with a photosensitive vinyl-containing compound and optionally maleic anhydride. The carboxyl groups are necessary so that when the photopolymer is exposed to light under a mask, the unexposed parts can be washed away with water or alkali solution.
This material does not contain ionic bonds. The polymer is not highly water dispersible and is not used as a water-based resin. U.S. Pat. No. 5,691,006 issued Nov. 25, 1997 to Salvin et al. for "Solder Resist Coating from Photosensitive Composition Containing Water as Solvent or Dispersant" discloses a composition comprising water soluble or dispersible, solid, film-forming polymers, photopolymerizable acrylate or methacrylate monomers or oligomers, and photoinitiator compounds. These compounds may be reacted with ammonia and/or amines which volatilize from the film formed when the material is cured.
None of the foregoing references appear to describe a composition which is radiation-curable and water-dispersible due to the presence of ionic bonds.
There is a need in the art for a single compound capable of being used as a coating material without being dispersed or dissolved in a solvent or capable of being dispersed in water, which can adhere to a wide variety of substrates, and be cured by ultraviolet or other radiation or heat or electron beam treatment in a very short period of time to a hard, tough and durable finish which is not soluble in water or other solvents such as toluene, acetone, gasoline and the like.